Adding a timer switch to a water heater (need electrical and contactor advice)

This is going to be my first instructable, but I need a little help first. This is the plan:

I'm going to wire a countdown wall switch to a contactor that is rated to handle the water heater. I know they sell direct water heater timers, but those are big and bulky. The are also set time of day timers. I want something that I can set that will turn off after a set time once the switch has turned on. I have found many wall switches that do exactly this, but they are not rated for such high currents. So, I will use a contactor to do the job.

The diagrams I have seen show the wall switch to be wired directly to the contactor. First question: Will the contactor pull only the power that is needed or do I need to add a resistor so that it will pull significantly less power?

In the same line of thought, would I save any power by using a contactor that has a coil rated much lower than line voltage and using a resistor for the wall switch to achieve it?

My water heater wired up to two 20 amp circuit breakers. Should I assume that 20 amps is the max resistive load for each heating element? If so, will this contactor suffice?


Thank you all.

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On the side of that relay you will see two contacts for the electro magnet that closes the switch connect your timer to that.

First, I have a timer wall switch on my attic fan. You turn the knob and set it to turn on the attic fan for a few minutes or a couple of hours. This will work great for what you are wanting to do. The current rating makes no difference since you will be using it with a contactor.

Now about the contactor. You can get a 20 amp contactor that uses a 120 coil. If you do then no transformers or resistors will be needed. Just use 120 volts through the timer switch to the contactor coil to turn the 240 water heater on and off all you want. And yes, 20 amps is the max load. Most water heater elements use about 10 amps or so.

One more thing, You could use a 12 0r 24 volt coil in the contactor but then you have to add a transformer which uses a bit of electricity itself and adds another component to increase the cost and possibly give problems in the future.

There are mechanical timer swiches that can handle 20 amps but they are hard to find and expensive. Use one of those and you really have a simple setup. It all depends on how much you want to spend.

One final word - thanks for at least giving this project a shot. We all started some where with a project that was over our head - It is just easy to forget that - unless we burned the house down. LOL
You should probably get in touch with a local contractor. Specifically an electrician. Modifying the water heater may violate local or regional laws. Not to mention an electrician can point you in the right direction so you don't cause a fire or kill yourself.
Jarun (author)  mpilchfamily3 years ago
I also want to state that I am here to learn. And I learn by doing. Getting someone else to wire it up for me wouldn't teach me anything as I must physically do it in order to learn. I might pick it up from watching, but that is also not nearly as much fun...

An electrician costs money, may or may not know the specifics of what I am asking about contactors depending on their expertise and experience, and one may already be on these boards and can answer my questions (or someone who already has the knowledge).
Jarun (author)  mpilchfamily3 years ago
Wow... um okay. Thank you for your concern. But I have experience with wiring. I am remodeling a portion of my house and this is included. I have moved and installed lighting fixtures and wall sockets. Everything is to code and nothing has burned down.

Also, I am not modifying the hot water heater itself, but the electrical wiring that leads to it. Very similar to the "Add a timer to your water heater" instructable that is already on this site.

Jarun (author) 3 years ago
This is an excellent resource site that explicitly explains what I want to do. I'm just double checking a few of the details. http://waterheatertimer.org/index.html